This invention relates to processes for preparing a phosphor pattern, the phosphor pattern prepared by the same and a back plate for a plasma display panel.
In the prior art, as one of flat plate displays, there has been known a plasma display panel (hereinafter referred to as "PDP") which enables multicolor display by providing a phosphor which emits light by plasma discharge.
In PDP, flat front plate and back plate comprising glass are arranged in parallel with each other and facing to each other, both of the plates are retained at a certain interval by a barrier rib provided therebetween, and PDP has a structure that discharge is effected in a space surrounded with the front plate, the back plate and the barrier rib.
In such a space, a phosphor is coated for display, and by discharge, the phosphor emits light by UV ray generated from filler gas, and the light can be recognized by an observer.
In the prior art, as a method for providing the phosphor, a method of coating a slurry solution or paste in which phosphors of the respective colors are dispersed, by a printing method such as screen printing has been proposed and disclosed in Japanese Provisional Patent Publications No. 115027/1989, No. 124929/1989, No. 124930/1989 and No. 155142/1990.
However, the above phosphor-dispersed slurry solution is liquid so that dispersion failure due to precipitation of the phosphors occurs easily, and the slurry solution also has a drawback that when a liquid photosensitive resist is used in the slurry solution, storage stability is poor due to acceleration of a dark reaction or the like. Further, the printing method such as screen printing is inferior in printing precision so that there are problems that it is difficult to cope with enlargement of a screen of PDP in the future, and others.
In order to solve these problems, there has been proposed a method of using a photosensitive element (which is also called as a photosensitive film) containing a phosphor (Japanese Provisional Patent Publication No. 273925/1994).
In the method of using a photosensitive element, only a phosphor-containing photosensitive resin layer of a photosensitive element comprising a photosensitive resin layer containing a phosphor and a support film is embedded in the space of the above substrate for PDP by contact bonding (lamination) under heating, the layer is subjected to imagewise exposure with active light such as UV ray by a photographic method using a negative film, an unexposed portion is removed by a developing solution such as an alkaline aqueous solution, and further unnecessary organic components are removed by calcination to form a phosphor pattern only at a necessary portion.
In the method using such a photosensitive element, the photographic method is used so that a phosphor pattern can be formed with good precision.
However, when a phosphor-containing photosensitive resin layer is formed on the above-mentioned substrate for PDP by using the photosensitive element, then imagewisely exposing active light through a photomask, and subjecting to development and calcination according to the conventional method, it is difficult to form a phosphor pattern with uniform thickness and shape over the surface of a concave portion surrounded by the wall surface of a barrier rib and the bottom of the space since the photocurability at the wall surface portion of the barrier rib which is inside surface of the concave portion which space becomes a discharging space is lower than that of the bottom of the substrate so that the photosensitive resin layer containing the phosphor at the wall portion of the barrier rib is liable to be eroded at development.